Bridgman Growth of New Nonlinear Optical Crystal (La1 − xSmx)3Ga5.5Nb0.5O14 for Quasi-Parametric Chirped Pulse Amplification

Samarium-doped La3Nb0.5Ga5.5O14 (Sm:LGN) crystals were grown along a (100)-orientation by the Bridgman method for quasi-parametric chirped pulse amplification (QPCPA) applications. The structure of La1-xSxmGN (x = 0.1, 0.2) crystals was the same as that of La3Nb0.5Ga5.5O14 (LGN) crystals. The effective segregation coefficient of Sm3+ in the La0.9Sm0.1GN crystal was 0.140. The full width at half maximum (FWHM) of La1-xSxmGN (x = 0.1,0.2) crystals was lower than 50″, which indicated the high quality of the crystals. The density of the La0.9Sm0.1GN crystal was 5.968 g/cm3 and that of the La0.8Sm0.2GNcrystal was 5.988 g/cm3. The transmittance of the crystals at 532nm and 800nm was all above 73%. The absorption spectra indicated that the crystals had strong absorption peaks at wavelengths of 1544 and 1595 nm. The thermal properties of La1-xSxmGN (x = 0.1, 0.2) crystals were similar to those of the LGN crystals. The laser damage thresholds of La0.9Sm0.1GN and La0.8Sm0.2GN crystals were, respectively, 188.30 and 54.84 TW/cm2 (@800 nm,35 fs).

A mathematical model for distribution of calcium in silicon by vacuum directional solidification

Calcium is one of the main impurity elements in silicon. The removal of calcium strongly affects the quality of the polycrystalline silicon ingot produced by a vacuum directional solidification method. Based on the considerations of the theory of segregation, mass transfer and evaporation during vacuum directional solidification process, a mathematical model for calcium distribution in silicon was proposed and it can be used to explain the removal mechanism. In order to confirm the mathematical model, an industrial scale experiment on UMG-Si with an initial purity of 99.98 wt. % was performed. Since the reaction temperature strongly influences both the evaporation and segregation of calcium, the dependences of effective segregation coefficient (keff) and the evaporation coefficient (kE) on temperature were carefully investigated. The results showed that the proposed mathematical model was highly consistent with the experimental data and the calcium removal efficiency mainly relied on the evaporation step.

Effect of Pulling Rate on Multicrystalline Silicon Ingot during Directional Solidification

In this paper, the structure and composition of multicrystalline silicon ingots prepared by directional solidification with different pulling rates were analyzed to investigate the effect of pulling rate on the multicrystalline silicon ingot. The results showed that the lower pulling rate will make the site taking place constitutional supercooling move to the upper part of ingots and make the high purity area become larger. Lowering the pulling rate will decrease the impurity effective segregation coefficient and the solid-liquid interface curvature.